1. Field of The Invention
The present invention relates to an apparatus and method for diagnosing a radiator fan control system installed in a vehicular internal combustion engine. Particularly, the present invention relates to the apparatus and method for diagnosing a cooling function of a radiator ran unit carried out by means of the radiator fan in the radiator fan control apparatus on the basis of a coolant temperature of an engine coolant.
2. Description of Background Art
Generally, an engine coolant is circulated through a vehicular internal combustion engine so as to cool the engine and is returned to a radiator. The coolant cooled by means of a heat exchange at the radiator is again circulated through the engine. This is called a water cooling type cooling system.
There is an automotive vehicle which is provided with a DC motor installed radiator fan unit in order to promote the heat exchange in the radiator.
A control unit is provided to perform an on-and-off control for the DC motor so that the cooling to the engine is appropriately carried out. In addition, a rotation speed of the DC motor is controlled at a plurality of stages so that a more precise temperature control for the engine coolant is achieved.
If, in the cooling system in which the DC motor installed radiator fan is installed, a broken line in a DC motor radiator fan driving system occurs and/or a failure occurs in a relay part of the DC motor radiator fan driving system, the radiator fan cannot be operated (driven to rotate) any more and, consequently, an excessive rise in the coolant temperature would be resulted even if a control signal from the control unit normally is output to: the DC motor.
Although it is possible, for the failure such as a broken line in the DC motor fan control system, to perform an electrical failure diagnosis, an occurrence in failure such as not to make a desired cooling through the radiator fan can be predicted. Therefore, an automotive industry has demanded to provide a diagnosing apparatus which is capable of determining whether the cooling by means of the radiator fan is actually carried out or not, or in other words, whether the radiator fan is normally functioning.